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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: rossverg on July 03, 2005, 06:55:30 PM

Title: Moles/Molar Calculations
Post by: rossverg on July 03, 2005, 06:55:30 PM

Hey everyone, I have a question which I think is probably easy but I have no idea how to do it.

I am familiar with the mole concept and I know it applies to this quesiton but I don't know how to answer it. I am also confused whetehr or not to take 1 mole of Nitrogen as 14.01g or 28.02g seeing as though Nitrogren exists as a diatomic molecule.

 

Calculate the mass of nitrogren in 28.02g of ammonium nitrate.

 
This is what I have done so far (but I don't know if it is even necessary :S

NH₄NO₃
Molar Mass = 14.01*2 + 1.008*4 + 16*3
                 = 80.052g

Then number of moles = mass/molar mass
                                 = 28.02/80.052
                                 = 0.35 mol



But now I'm not sure what to do next....

Thanks to all in advance.

Title: Re:Moles/Molar Calculations
Post by: xiankai on July 03, 2005, 07:06:36 PM

since u are measuring nitrogen as an atom, not as a gas, u are on the right track. :)

now about the procedure. first find the % mass compostion of N in NH4NO3. which is, the Mr of all the N atoms divided by the Mr of NH4NO3. with the value got, multiply it with the weight of NH4NO3 and your answer is there.

Title: Re:Moles/Molar Calculations
Post by: rossverg on July 03, 2005, 07:16:27 PM

Oh I see. Thanks for the qyuick reply Xiankai!  :D

So this how how I do it:

Mr of NH4NOE
       
        N:H:O
        2:4:3

Therefore there are 2/9 Nitrogren atoms

so 2/9 * 28.02

= 6.28g of Nitrogen   :-\

Title: Re:Moles/Molar Calculations
Post by: DrCMS on July 04, 2005, 03:59:05 AM

No.  You need to use the atomic mass of each atom as you did orginally and then multiply by the weight of the sample.

Title: Re:Moles/Molar Calculations
Post by: xiankai on July 04, 2005, 04:42:39 AM

u r calculating my mole compositiom and not mass composition like i stated earlier :/

Title: Re:Moles/Molar Calculations
Post by: arnyk on July 04, 2005, 03:00:57 PM

For every 1 mol of ammonium nitrate there are 2 mol of N.  Therefore if you have 0.35 mol of NH4NO3, you will have 0.7 mol of N.

Convert moles to mass.